An X-ray diagnostic system radiates an X-ray to a subject such as a patient, detects the X-ray transmitted through the subject, and collects the dose distribution data of the detected X-ray (X-ray transmission data) by use of a data collector. Thereafter, the X-ray diagnostic system performs a reconstruction process on the dose distribution data, and creates a slice image (tomographic image) of the subject. An exemplary one developed as this X-ray diagnostic system is an X-ray CT system (X-ray computed tomography system) configured to take radiographs of a subject with an X-ray radiator and an X-ray detector opposed to each other with the subject therebetween and rotated around the body axis of the subject.
The X-ray diagnostic system like this is configured to collect scanograms (positioning images) by taking radiographs without rotating the X-ray radiator or the X-ray detector for the purpose of setting a scanning range before radiographing such as multi-slice scanning or helical scanning. Among X-ray diagnostic systems of this type, there has already been a product which includes auto exposure control (AEC) configured to convert the thickness of each bodily part into a water equivalent thickness by use of the scanograms, and to determine a tube current value (mA) on the basis of a specified SD (Standard Deviation).
The AEC automatically calculates, from the scanograms, an X-ray dose suitable for the bodily thickness of each part of the subject, and thereafter finely controls the x-ray dose, namely a tube current, for each rotation of the X-ray radiator and the X-ray detector. This realizes a reduction in radiation exposure by inhibiting unnecessary radiation exposure while maintaining high-quality images.
Although, however, the above-described technology adjusts the tube current in accordance with the size (bodily thickness) of the subject, the tube current determined through the adjustment is merely adjusted within a limited range of a maximum value and a minimum value determined by the system capacities. This is likely to cause artifacts such as an overflow artifact (an artifact appearing on a reconstruction image due to an excess over the maximum value of a count which can be handled in the data collector) and an artifact dark-band artifact (an artifact appearing on a reconstruction image due to a shortage in an X-ray dose, namely a shortage in a raw data count). This artifact degrades the image quality of X-ray images such as tomographic images.